Modern civilization produces a large quantity of organic waste. It originates from household, commercial, institutional, and industrial waste and can include materials such as sewage sludge, animal manure, potato skins, slaughterhouse runoff, and so forth.
One of the biggest sources of organic waste is sewage material. Sewage material refers broadly to sewage sludge, dewatered sewage, animal waste, lagoon sludge, and the like. Sewage material is most commonly produced by wastewater treatment processes such as those used in municipal sewage treatment plants, large scale animal production facilities, and the like.
Sewage material contains valuable nutrients that would be desirable to capture and use in a safe and renewable manner such as in fertilizer. Transforming sewage material from waste into a valuable resource produces tremendous environmental benefits. The alternative is to dispose of the sewage material in less desirable ways such as incineration or deposition in a landfill, lagoon, or the ocean.
Unfortunately, there are a number of obstacles that have prevented the widespread use of sewage material for fertilizer. One of the biggest obstacles is the presence of toxic materials in the fertilizer such as heavy metals, pathogens, drug residues, and the like. These materials originate with the sewage material and are difficult to remove when it is processed to make fertilizer. Other obstacles include the potential for applying too much or too little of each nutrient and the possible detrimental effects on water quality from leaching, erosion, or runoff losses.
Regulatory restrictions have been placed on the use of fertilizer derived from sewage material due to these obstacles. There are restrictions that prevent the fertilizer from being used on land that exceeds a certain slope or has certain soil conditions. There are restrictions on how close it can be applied to homes, wells, streams, roads, and property lines. There are also restrictions that limit the quantity of heavy metals (arsenic, cadmium, chromium, cobalt, copper, mercury, molybdenum, nickel, lead, selenium, and zinc) that can be applied to a given area. Once these limits are reached, no more fertilizer can be added, but the land can still be used for normal crop production.
Numerous attempts have been made over the years to develop a process to dispose of organic waste materials in an effective and cost efficient manner. Unfortunately, most of these processes consume large amounts of energy, emit noxious gases, and rarely achieve the desired conversion rate.
An earlier process oxidized the waste material in a solution of nitric and sulfuric acid. The reaction occurred in a pressurized reactor that was maintained at a temperature of no more than 210° C. Oxygen gas was added to facilitate the reaction and breakdown of the waste material.
The process successfully transformed the waste material into materials such as oxygen, nitrogen, water, carbon dioxide, and so forth. However, the solution included a high concentration of nitric and sulfuric acid and much of it was consumed in the process. This made the economics of the process challenging since it consumed large amounts of relatively expensive acid and produced mostly low value end products.
A number of embodiments of an improved process for eliminating waste material and/or transforming it into a commercially valuable end product are described below. The process is especially suited for converting sewage materials into fertilizer and other useful materials. The process reduces or eliminates many of the problems and disadvantages associated with conventional processes.